The expired U.S. Pat. No. 4,316,048, (hereinafter the “'048 Patent”) by inventor Jerry M. Woodall proposes employing a large insulated area of silicon, which, when melted, stores energy as heat of fusion energy. This concept is also known as a phase change battery (PCB). In the '048 Patent, the silicon or other phase change material, is melted by the sun's rays introduced through a solar concentrator, which transfers concentrated solar energy to the phase change material. The phase change material transitions from a molten state to a solid state, emitting latent heat energy and photon power transfer at a constant temperature while in a molten state and molten-solid state. Electrical energy is created from a photovoltaic cell positioned at a location near the PCB so that it receives radiant heat energy from the phase change material. Greater efficiency of heat to electricity conversion is afforded by using a combination of a thermal-to-radiant-energy directional emitter and a band pass filter, which together operate to permit the passing of only a certain range of photon energies to which the photovoltaic cell is most responsive.
U.S. Pat. No. 4,389,533 issued to Ames describes a photovoltaic device including a solar panel and a container housing a phase change material positioned together so that heat generated during operation of the cells in the panel will melt the phase change material, thereby storing heat and lowering the operating temperature of the cells. However, the photovoltaic array is also producing electricity while simultaneously melting the phase change material. The heat absorbed by the phase change material is used to provide heat, rather than electricity, during night time hours. The primary objective of Ames is to remove heat from the photovoltaic array, especially during peak daylight hours when the array is hottest. A drawback to Ames is that its solution of storing the heat in a phase change material would not work for the hottest parts of the country, or in Summer, when households require cooling, even at night.
United States Patent Publication No. 2015/0256119 to Datas Medina et. al discloses, an energy storage system comprising a vessel made of a refractory material and containing a phase change material, a thermally insulating cover at least partially surrounding the vessel, an emitter made of a refractory material, the emitter having a first side arranged to be heated by the phase change material and a second side intended to radiate thermal power, at least one photovoltaic cell arranged to receive the thermal power emitted by the second side of the emitter, and electric means for heating the phase change material. This reference therefore discloses the use of a PV array directed to receive thermal radiation from a phase change material and convert it into electricity. This reference proposes melting the phase change material using methods including resistive heaters and magnetic means. This reference furthermore discusses using a PV array to generate electricity solely from thermal radiation produced from the melted phase change material.
U.S. Pat. No. 5,932,029 issued to Stone, et al. proposes a system whereby a phase change material such as silicon is heated using focused and concentrated sun rays. The thermal radiation from the phase change material is then processed to extract a band-width which is most efficient for the conversion of thermal energy to electrical energy by a PV array. This system is specifically designed for high-efficiency electrical energy production during times of darkness, such as during an eclipse or during times when sunlight is unavailable and specifically has applications to space vehicles.
This system also employs a cooling sub-system which reduces overall efficiency by removing heat from the PV array; heat that could have been stored in the phase change material and converted to electrical energy. Rather, this system must input energy to circulate cooling fluid through the PV array, so that it performs at a reasonable efficiency level. Moreover, this patent does not propose using a PV array to both melt the phase change material and produce electricity from the sun during daylight hours.
What is apparent, is that the art has not addressed using a PV cell that produces electricity during the day, while introducing energy to melt a phase change material and then using a PV cell at night to produce electricity from latent heat energy radiating from the phase change material.